The present invention relates to a copolymer with a high dielectric constant which is used in thick film electroluminescence elements and thin capacitors, and to a method of producing the copolymer.
In so-called thick film electroluminescence elements, a luminous layer comprising a polymer matrix and fluorescent powder such as ZnS (Cu) or the like, which is dispersed in the polymer matrix, is used. Cyanoethylated cellulose, cyanoethylated polyvinyl alcohol or the like, which has a high dielectric constant, is used as the polymer matrix from the viewpoint of a decrease in the driving voltage.
However, since conventional polymers such as cyanoethylated polyvinyl alcohol and the like, all of which have high dielectric constants, are produced by a method in which acrylonitrile is reacted with polyvinyl alcohol in the presence of a basic catalyst so as to introduce cyanoethyl groups into polyvinyl alcohol by the substitution of the hydrogen of the hydroxyl groups thereof, 10% or more of the hydroxyl groups necessarily remain unsubstituted in its repeating unit. The conventional polymers with high dielectric constants have a critical problem with respect to their high hygroscopicity due to the residual hydroxyl groups.
It is considered that the polymer used in the luminous layer of a thick film electroluminescence element preferably has a low level of hygroscopicity from the viewpoint of its life of luminescence.